You could do it the old fashioned way. You find somebody who thinks the value of their crypto will go up. You pay them to borrow their crypto for, say, a year. You then sell the crypto for dollars and in a year you hope you can buy it back for less than you made.
The legal way to do it would be with an old-fashioned paper contract between two known parties. But as web3isgoinggreat.com has made clear to me, the more effective way to do it is to use some crypto site for the deal. If you're lucky, the tools/sites/curriencies you've used will just have gone out of business. And even if not, apparently you can just say, "Oops, I used the money to do other things so I'm not giving anything back to you."